1. Field of the Invention
The present invention relates to a magnetic memory device and a manufacturing method thereof and, more particularly, to a magnetic memory device which performs write by a current magnetic field every bit and reads out information of “1” or “0” in response to a resistance change corresponding to the magnetization state of a cell, and a manufacturing method thereof.
2. Description of the Related Art
MRAM (Magnetic Random Access Memory) utilizing the magneto resistive effect have recently been proposed as a memory element. The feature of the MRAM is that to write data in a memory cell, the magnetization direction of a ferromagnet is changed using a current magnetic field. Of MRAM, an MTJ (Magnetic Tunneling Junction) element using the TMR (Tunneling Magneto Resistive) effect can extract information of “1” or “0” in response to a change in resistance value. The MR (Magneto Resistive) ratio of the MTJ element as a resistance difference between “1” and “0” almost reaches 50%, which greatly promotes the practical use of MRAM.
To generate an information writable current magnetic field in a memory cell having a magneto resistive element such as an MTJ element, a sufficiently large write current must be supplied to write wiring. At present, the write current reaches about several mA to 10 mA per write wiring line. A further shrink in feature size shortens the distance between magneto resistive elements. This means generation of a large write current influences cells adjacent to a selected cell.
One of techniques which solve this problem is “magnetic shield”. According to this technique, only current magnetic field wiring or both current magnetic field wiring line and a magneto resistive element are covered with a magnetic member. A magnetic field generated by the current magnetic field wiring is concentrated on a selected cell by the same effect as that of a yoke. Information can be written in the selected cell by a small write current.
A known example of this technique is one disclosed in Jpn. Pat. Appln. Publication No. 11-238377. In this example, as shown in FIG. 61, element isolation oxide films 72 are selectively formed on a semiconductor substrate 71. A MOSFET 73 is selectively formed between the element isolation oxide films 72. The source/drain diffusion layer of the MOSFET 73 is connected to a GMR (Giant Magneto Resistive) element 80 via contacts 74, 76, and 78, and first, second, and third wiring layers 75, 77, and 79. Upper and lower word lines 81 and 82 for writing information in the GMR element 80 by a current magnetic field are formed above and below the GMR element 80 at intervals from the GMR element 80. A magnetic shield layer 83 made of a nonconductive ferrite material is formed as a passivation film which covers the entire surface of a memory cell array.
The prior art can shield a stray magnetic field outside the magnetic shield layer 83 by the non-conductive ferrite material. The prior art can also concentrate a magnetic field generated by the write wiring lines 81 and 82 on the magnetic layer of the GMR element 80 serving as a recording portion.
The prior art, however, has a poor effect of preventing erroneous write caused by a magnetic field which leaks between adjacent cells in a downsized magnetic memory. The prior art cannot satisfactorily concentrate a magnetic field by the current magnetic field wiring on the magnetic member.